1 090 



HI' MAN ANATOMY. 



Molecular layer 

 Granule layer 



White matter 

 ^ Cells of Purkinje 







part of the dentate nucleus. Since the latter and the embolus are likewise slightly 

 connected, it is evident that all four internal nuclei are more or less continuous 

 masses of .gray matter. 



In structure the internal nuclei differ markedly from the cerebellar cortex, 

 since in the main they are composed of irregularly disposed nerve-cells of one kind 

 interspersed with numerous nerve-fibres. The dentate nucleus contains cells from 

 .020-.030 mm. in diameter whose bodies are angular or stellate in outline and pig- 

 mented in varying degrees. Their processes are usually so disposed that the axones 

 pass into the medullary substance enclosed by the plicated lamina and the dendrites 

 into the surrounding white matter of the hemisphere. Numerous fibres enter the 

 dentate body from without, many being the axones of the Purkinje cells, and break 

 up into a rich plexus within the folded sheet of gray substance. Since the nucleus 

 emboliformis and the nucleus globosus are only incompletely isolated parts of 

 the dentate nucleus, their structure corresponds closely with that of the chief mass. 



The roof-nuclei, on the 



FIG. 943. contrary, possess cells of 



much larger size (.040 to 

 .080 mm.), more rounded 

 form and greater uniform- 

 ity in tint, although their 

 general yellowish brown 

 color implies less intense 

 pigmentation. Numerous 

 strands of nerve-fibres sub- 

 divide the nucleus into 

 secondary areas, while 

 some large transversely 

 coursing bundles establish 

 a decussation with the roof- 

 nucleus of the opposite 

 side. 



The Cerebellar 

 Cortex. When the folia 

 are sectioned at right 

 angles to their course, each 

 leaflet composing the 

 characteristic arborization 

 is seen to consist of a cen- 

 tral tract of white medul- 

 lary substance, covered in 

 by the continuous super- 

 ficial sheet of cortical gray 

 matter. The latter, usually somewhat less than one millimeter in thickness, includes 

 two very evident strata the outer and lighter molecular layer and the inner and 

 darker grannie layer. 



The molecular layer is of uniform thickness, about. 4 mm., and contains three 

 varieties of nerve-cells the Purkinje cells, the basket cells and the small cortical 

 cells. The Purkinje cells, the most distinctive nervous elements of the cerebellum, 

 occupy the deepest part of the molecular layer, where they are disposed in a sing It- 

 row along the outer boundary of the subjacent granular layer. The cells are most 

 numerous and more closely placed upon the summit of the folium and fewer and 

 more scattered aloni; tin- fissures, in which situation they are also often of less typical 

 pyriform shape. They possess a large flask-like body, about .060 mm. in diameter, 

 from the pointed and outwardly directed end of which usually one, sometimes more, 

 robust dendritic process arises. The chief process, relatively thick and very short, 

 soon divides into two branches, which at first diverge and run more or less horizontally 

 and then turn sharply outward to assume a course vertical to the surface and undergo 

 repeated subdivision. Tin- arrangement of the larger dendrites is very striking and 

 recalls the branching of the antlers of a deer. The smaller processes arise at varying 



jji 1 



-,..!__ ..---' ^ \ Central limb 



of white matter 



Transverse section of cerebellar folium, showing relations of cortex to 

 underlying white matter. X 10. 



